This application relates to a speed change mechanism wherein a cam groove transfers rotation between an input and output shaft, and achieves the speed reduction.
Speed reducers are utilized to achieve a distinct rotational speed at an output shaft relative to an input shaft. In many applications, an input speed of a particularly high value is reduced to a lower speed for an output application. This may happen, as an example, in an automotive application wherein the input speed is somewhat dependent on the engine speed, or on the speed of a particular motor. On the other hand, in some instances it is desirable to increase the speed between the input and the output shaft.
In the past, various gearing mechanisms have been utilized wherein the number of teeth on input and output gear sets are selected to achieve a predetermined speed change. Speed reducers have often utilized planetary gearbox arrangements. This is sometimes somewhat limited in that the output rotational direction cannot be changed, and the potential size of the speed reducer limits the amount of speed reduction available. Further, high noise and vibration due to gear tooth meshing often occurs.
In a disclosed embodiment of this invention, a change speed mechanism includes a cam driver associated with an input shaft and a cam follower associated with an output shaft. A moving member connects the cam driver to the cam follower. The cam driver and cam follower each have a cam groove with a generally sinusoidal shape. The number of peaks and valleys in the follower and driver are different. If the device is to be a speed reducer, then the cam follower will have more peaks and valleys than the cam driver. On the other hand, if the mechanism is utilized to increase speed, the reverse would be true.
A pin is mounted in the moving member and engaged in the groove in the cam driver. As the cam driver turns, it causes the pin and the moving member to move axially. A pin at another end of the moving member is received in the groove in the cam follower. As this second pin moves, it moves through the groove in the cam follower, and causes the cam follower to rotate. In this way, rotation is transmitted from the cam driver to the cam follower. By controlling the number of peaks and valleys in the respective grooves in the cam driver and cam follower, a desired speed change is achieved. For purposes of this application, the application will be described as a speed reducer. However, a worker in this art would recognize that by simply reversing the arrangement of parts, a speed increase device could also be achieved.
The pins in the cam follower and cam driver grooves are positioned at approximately equal positions. Further, a second moving member having pins engaged in a second cam groove in both the driver and cam follower is also operating in a similar fashion to the initial moving member and its pins. The second moving member typically has its pins somewhat offset from the pins of the first moving member. In this way, the cam follower tends to be driven even at the extreme ends of the first moving member, at which there might otherwise be a short break in rotation. That is, the second moving member acts to continue to drive the cam follower at the extreme ends of the sinusoidal peaks in the first grooves.
These and other features of the present invention can be best understood from the following specification and drawings, the following which is a brief description.